ATOMIC RADIUS Radius is the distance from the center of the nucleus to the “edge” of the electron cloud. Atomic radii are usually measured in picometers (pm) or angstroms (Å). An angstrom is 1 x 10 -10 m.
ATOMIC RADIUS BROMINE = Br 2 Since a cloud’s edge is difficult to define, scientists use define covalent radius, or half the distance between the nuclei of 2 bonded atoms. 2.86 Å 1.43 Å
ATOMIC RADII TRENDS As you go down a family the n value increases making the radius larger. DOWN A FAMILY OR GROUP WHY? INCREASES
ATOMIC RADII TRENDS As you go across a period the number of protons increases, (nuclear charge) pulling the electrons in tighter making the radius smaller. ACROSS A PERIOD WHY? DECREASES
IONS - remember Metals Lose electrons becoming positive. Calcium – Ca [Ar]4s 2 Loses 4s 2 e - s becoming Ca +2 and [Ar] Noble gas Configuration. (Octet Rule) Nonmetals Gain electrons becoming negative. Chlorine – Cl [Ne]3s 2 3p 5 Gains one e - becoming Cl -1 and [Ar] Noble gas configuration. (Octet Rule)
IONS – How can I remember? Metals Nonmetals This is Ann ion - ANION She is unhappy and negative. This is Cat-ion - CATION He is a “plussy” cat!
IONIC RADII TRENDS As you go down a family the n value increases making the radius larger. DOWN A FAMILY OR GROUP WHY? INCREASES
IONIC RADII TRENDS For the metals the nuclear charge is greater than then number of electrons pulling them in tighter making the radius smaller. At the nonmetals the radius gets larger because the ion has gained electrons. ACROSS A PERIOD WHY? DECREASES then INCREASE
NONMETALLIC ATOM AND ION COMPARISON Why do the Noble Gases not have an ionic Radius?
ATOM AND ION COMPARISON Why does Hydrogen not have an ionic Radius?
As more electrons are added to atoms, the inner layers of electrons shield the outer electrons from the nucleus. The effective nuclear charge on those outer electrons is less, and so the outer electrons are less tightly held Shielding Effect
The energy required to remove an electron from an atom is ionization energy. (measured in kilojoules, kJ) Ionization Energy
IONIZATION ENERGY The larger the atom is, the easier its electrons are to remove. Ionization energy and atomic radius are inversely proportional. Ionization energy is always endothermic, that is energy is added to the atom to remove the electron.